But during his campaign, he touted the adviser, George Papadopoulos, as an "excellent guy" as he sought to beef up his foreign policy staff.

"The Fake News is working overtime. As Paul Manaforts [sic] lawyer said, there was 'no collusion' and events mentioned took place long before he came to the campaign. Few people knew the young, low level volunteer named George, who has already proven to be a liar. Check the DEMS!" Trump tweeted.

The Fake News is working overtime. As Paul Manaforts lawyer said, there was "no collusion" and events mentioned took place long before he...

On Monday, former Trump campaign chairman Paul Manafort and his deputy, Rick Gates, surrendered to Justice Department special counsel Robert Mueller and pleaded not guilty to several charges, including conspiracy against the US. It was also announced that Papadopoulos, had pleaded guilty earlier this month to making a false statement to the FBI after he lied about his interactions with foreign officials close to the Russian government. The revelation is the campaign's clearest connection so far to Russia's efforts to meddle in the 2016 election.

Trump declined to answer questions from reporters Tuesday about Papadopoulos or Manafort after he made remarks about his tax reform efforts at the White House.

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The White House has sought to distance itself from the three men. Officials have said Manafort and Gates' alleged activities happened before the campaign, and has said Papadopoulos was not a part of the campaign's inner workings.

The fact that Papadopoulos was unpaid puts him in line with many on Trump's campaign and in no way gauges his stature in the operation.

According to previous reporting, Manafort, Gates, Trump son-in-law Jared Kushner and senior strategist Steve Bannon were all unpaid "volunteers" while doing extensive, high-level work for the campaign.